Loud-speaker with flexible diaphragm mounting



July 10, 1951 A. L. WITCHEY I LOUD-SPEAKER WITH FLEXIBLE DIAPHRAGMMOUNTING Filed March 25, 1948 l ENTOR -ALBERT L.WITEHEY ATTO R N EYPatentecl July I0, 1951 LOUD-SPEAKER WITH FLEXIBLE DIAPHRAGM MOUNTINGAlbert L. Witchey, Merchantville, N. J., assignor to Radio Corporationof America, a corporation of Delaware Application March 25, 1948, SerialNo. 17,039

Claims. 1

This invention relates to acoustic devices, and more particularly to animproved loudspeaker construction having direct radiating diaphragms ofthe piston type.

Heretofore, dynamic type loudspeakers have voice coil with respect tothe air gap in the mag- This usually has been accomnet structure.plished by employing, in addition to the peripheral support for thediaphragm, a separate, corrugated, flexible disc having its outer edgeattached to a rigid, adjustable support and its inner edge attached tothe center portion of the diaphragm adjacent to the voice coil.

The principal object of my invention is to provide an improvedloudspeaker construction using a cone type diaphragm and having smalleroverall dimensions than and an improved response over similar prior artloudspeakers.

It is also an object of my invention to provide an improved loudspeakerconstruction as aforesaid in which the conventional or customary dishpansupport for the loudspeaker diaphragm is dispensed with while stillproviding adequate peripheral support for the diaphragm.

Another object of my present invention is to provide an improvedloudspeaker as above set forth in which the same means which supportsthe inner or apex end of the diaphragm is also utilized to support theouter or peripheral edge thereof.

According to my present invention, I provide a new loudspeakerconstruction using a cone type diaphragm by eliminating the use of thecustomary housing or dishpan support for the diaphragm. In accordancewith my invention, I provide a single element suspension means forloudspeaker diaphragms which will support the diaphragm both at its baseand at the center without extending beyond the outer circumferentiallimits of the diaphragm. In addition to supporting the diaphragm, thesuspension element also functions as a means for centering the voicecoil with respect to the air gap provided between the poles of themagnet structure.

The suspension means of my invention, according to a preferredembodiment, consists of a In addition to the base flexible, annular dischaving its outer edge attached to the base of the diaphragm and itsinner edge attached to the center portion of the diaphragm. Thesuspension means is supported intermediate its inner and outer edges byan annular ring adjustably carried by the field structure of theloudspeaker, thereby providing a suspension which is disposed entirelywithin the outer circumferential limits of the diaphragm. I have alsoprovided a housing for covering the magnet structure and rear portionsof the speaker diaphragm. The housing comprises a cylindrical case openat one end and having its closed end attached to the magnet structure,while the edge of the open end is disposed in spaced relationto theouter edge of the diaphragm in such a manner that the diaphragm andhousing together form an acoustic chamber.

7 More specifically, I have provided a new loudspeaker constructionwhich minimizes the overall dimensions thereof, one that provides, animproved response, is highly efficient, easy to construct, andeconomical to manufacture.

The novel features of my invention, both as to its organization andmethod of operation, as well as additional objects and advantagesthereof, will best be understood from the following detailed descriptionof two embodiments thereof, when read in connection with theaccompanying drawing, in which Fig. 1 is a plan view of a loudspeakerconstructed in accordance with a preferred form of my present invention,

Fig. 2 is a sectional view thereof, taken along the line 22 of Fig. 1,

Fig. 3 is a plan view of the field structure shown in Fig. 2, and

Fig. 4 is a plan view in section of a second embodiment of my presentinvention taken on a plane through the diaphragm perpendicular to itsaxis, and illustrating another form of diaphragm support according to myinvention.

Referring more particularly to the drawing, there is shown, in Figs. 1and 2, a loudspeaker I having a diaphragm 3, a magnetic field structure5 for efiecting vibration of the diaphragm in accordance with audiofrequency currents passing through the voice coil of the diaphragm, anda housing 1 for the elements of the loudspeaker.

The loudspeaker diaphragm 3 is a direct radiating diaphragm of thepiston type, that is, the type where the central portion is stiffened sothat the diaphragm moves as a whole at low frequencies. The diaphragm ismade from a material suitable for sound radiation, as, for example, ahard finish paper or other fibrous material. The diaphragm comprises afrustroconical center portion 9, and an outwardly flared portion l Iextending from the center portion and curved backward so as to providean outwardly flared and bowed sound reproducing surface, the portion llterminating in a peripheral or outer edge l3. In other words, thediaphragm may be described as substantially semi-toroidal, that is, asurface generated by the rotation of a semi-circular are about an axisparallel to the radius of th are which is perpendicular to its corddiameter. Attached to the center portion 9 of the diaphragm as bycementing or otherwise, is a cylindrical coil form 15 which carries avoice coil II. The diaphragm is also provided with a dust cap I8,preferably of paper, which is attached adjacent the center portion 3 forclosing the opening provided by the center portion.

The field structure consists of a U-shaped yoke 21 and an outer polemember 23 attached at its ends to the yoke by welding or other suitablemeans 25. Within the yoke structure, there is a center core 2'! which isconstructed in two parts both of which are circular in cross section.The lower or base portion 29 of the core is preferably constructed ofpermanent magnet material having extremely high retentivity, such asAlnico V, composed of the following elements: aluminum 8 percent, nickel14 percent, cobalt 24 percent, copper 3 percent, and the remainder iron.The upper portion or inner pole piece 3! of the center core is made ofmaterial such as soft iron or mild steel, or other material possessing ahigh degree of permeability, and has a base or shoulder portion 32 andan upper portion 33.

The center core or pole piece 21 is of suiiicient length so that thelower face 34 of the base portion 29 will rest on a flat surface 35 onthe bottom of the yoke 2|, and the inner pole piece 3! will extend intoan aperture 3? in the outer pole member 23. The aperture 57 is ofsuiiicient size so that an air gap 39 is provided between the peripheryof the aperture and the inner pole piece 2?.

In assembling the U-shaped yoke 2| and the center core or pole piece 27,I have provided a spring clip 4| of the type disclosed in the copendingapplication of David H. Cunningham, Ser. No. 632,064, filed November 30,1945, and nowfPatent 2,501,031. The spring clip ii is made of resilientmaterial and has (1) two leg portions '43 and 45 which will rest againstthe outer pole member 23, and (2) a central portion 4? which connectsthe leg portions and which bears against the base or shoulder portion 32of the inner pole piece portion 33 and firmly holds the center core 21in assembled relation with the yoke 2|. The central portion 'll of thespring clip is provided with an aperture 49 through which the upperportion 46 of the inner pole piece 3| extends.

For the purpose of accurately centering the inner pole piece 3! in theaperture 31', I have provided a sheet metal centering disc 5i,preferably of tress which is permanently secured to the outer polemember 23 by any suitable means, as by welding 52. The centering disc isalso provided with an aperture 53 concentrically disposed with respectto the aperture 3'! and through which the inner pole piece 3| may beinserted for centering in the aperture 31.

In order to freely suspend the diaphagm and support the voice coil l? inits proper relationship to the field structure 5, I have provided asingle element, flexible support or member 55 which consists of anannular, corrugated disc of conventional web material having a highdegree of compliance in the axial direction of diaphragm movement andonly a limited degree of compliance perpendicular to the axial directionof diaphragm movement. The flexible support or disc 55 has inner andouter edges 51, 59 which are cemented or otherwise suitably attached,respectively, to the peripheral edge 13 of the outwardly flared portionH and the inner edge 5| of the center portion 9 of the diaphragm,disposing the peripheral edge [3 and the inner edge 6| in'a common planesubstantially perpendicular to the axis of the diaphragm. The flexiblemember 55 is constructed with an intermediate portion 63 between itsinner and outer edges 57, 59 which is cemented or otherwise suitablyattached to an annular brass ring member 65, and which divides theflexible member into inner and outer portions 64, 65. The annular member65 is adjustably mounted on top of the outer pole member 23 by twoscrews 61, 69 which are inserted through holes ll, l5, respectively, inthe outer pole member 23. The holes H, 73 are sufficiently large topermit lateral adjustment of the ring member for centering the voicecoil I! in the air gap 39.

In order to facilitate adjustment of the ring member and to provideaccess to the screws 67, 59 I have provided holes l5, iii in the sprinclip ll and holes l5, 8| in the base of the U-shaped yoke 21, the holesH, '55, and 19 being concentrically aligned and the holes 73, TI, 8!also being concentrically aligned.

The field structure ii is enclosed in a cylindrical housing I open atone end 53. The housing is removably attached to the base of theU-shaped yoke 2! by means of a bolt 85. The housing "I is constructed sothat a space 8'! will be provided between the edge 89 of the open end 83thereof and the peripheral edge l3 of the diaphragm to permit soundwaves generated by the back of the diaphragm to be released from theacoustical chamber 9! formed by the diaphragm 3 and the housing 1.

While I have described a preferred form of my invention, it willundoubtedly be apparent to those skilled in the art, that many otherforms thereof are possible within the spirit of my invention. Forexample, as illustrated in Fig. 4, in place of the single element,flexible, corrugated disc 55 used to support the outwardly boweddiaphragm 3, a plurality of radially extending supports 93 may be usedto support the diaphragm in a manner similar to the single elementsupport 55. It will, therefore, be seen that, by eliminating theconventional dishpan support and providing an outwardly bowed diaphragmfor the loudspeaker, I have provided a loudspeaker having smaller thanusual overall dimensions. My improved loudspeaker construction alsopermits the use of a diaphragm having a larger vibrating surface thanhas been used customarily in prior art loudspeakers of equivalent size,wherefore the loudspeaker of my present invention is capable ofproviding an improved response.

While I have illustrated but two modifications of my invention, variousother modifications and changes will, no doubt, readily suggestthemselves to those skilled in the art. I therefore desire that theparticular form of my invention described herein shall be considered asillustrative and not as limiting.

associated with said center portion for vibrating said diaphragm, and anannular flexible supporting member disposed between said center andoutwardly flared portions attached adjacent the peripheries thereof,said annular flexible supporting member being supported intermediate itsinner and outer edges from said driving means.

2. An acoustic device according to claim 1, characterized in that saidsup-porting member has inner and outer edges disposed in a common planesubstantially perpendicular to the axis of said diaphragm.

3. An acoustic device according to claim 1, characterized b the additionin said device of a cylindrical housing open at one end, said housingbeing carried by said driving means and having its open end terminatingin spaced radial relation to said outwardly flared portion, and furthercharacterized in that said housing and said diaphragm together form anacoustical chamber.

4. In an acoustic device, a diaphragm of the piston type having afrustro-conical center portion and an outwardly flared portion extendingfrom said center portion, the inner and outer edges disposed in asubstantially common plane perpendicular to the axis of said diaphragm,flexible supporting means for said diaphragm connecting said inner andouter edges, said means being fixedly supported intermediate the pointsof connection to said inner and outer edges, and driving means for saiddiaphragm operatively associated with said inner edge for vibrating saiddiaphragm.

5. An acoustic device according to claim 4, wherein said driving meansincludes a field structure, wherein said diaphragm, said supportingmeans, and said field structure are provided with a cylindrical housinghaving one end open, and wherein said housing is carried by said fieldstructure and has said open end terminating in spaced radial relation tosaid outer edge of said diaphragm.

6. In an acoustic device, a diaphragm having a frustro-conical centerportion and an outwardly flared and bowed portion extending from saidcenter portion, said diaphragm terminating in inner and outer edgeslying in substantially the same plane perpendicular to the axis of saiddiaphragm, a flexible support for said diaphragm, said support beingconnected to said diaphragm at points adjacent to said inner and outeredges, and driving means associated with said diaphragm for vibratingsaid sound reproducing surface.

7. In an acoustic device, a diaphragm of the piston type having afrusto-conical central portion and an outwardly flared portion extendingfrom said central portion, flexible supporting means for said diaphragmdisposed entirely within the outer limits of said outwardly flaredportion and attached to said central and outwardly flared portions, saidflexible supportin means comprising a single element, flexible discfixedly supported intermediate the points of attachment thereof to saidcentral and outwardly flared portions, and driving means for saiddiaphragm operatively associated with said central portion.

8. In an acoustic device, a diaphragm of the piston type having afrusto-conical central portion and an outwardly flared portion extendingfrom said central portion, flexible supporting means for said diaphragmdisposed entirely within the outer limits of said outwardly flaredportion and attached to said central and outwardly flared portions, saidflexible supporting means comprising a plurality of radially extendingflexible supports each of which is fixedly supported intermediate thepoints of attachment thereof to said central and outwardly flaredportions, and driving means for said diaphragm operatively associatedwith said central portion.

9. In an acoustic device, a diaphragm having a frustro-conical centerportion and an outwardly flared portion extending from said centerportion, said diaphragm terminating in inner and outer edges lying insubstantially the same plane perpendicular to the axis of saiddiaphragm, a plurality of radially extending flexible supports for saiddiaphragm, said supports being connected to said diaphragm at pointsadjacent to said inner and outer edges, and driving means associatedwith said diaphragm for vibrating said sound reproducing surface.

10. An acoustic device according to claim 9, characterized in that saidradially extending diaphragm supports are disposed in circumferentialspaced relation to each other about said axis of said diaphragm.

ALBERT L. WITCHEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,878,018 Stephens Sept. 20, 19321,984,550 Sandeman Dec. 18, 1934 2,084,945 Cornwell June 22, 19372,269,284 Olson Jan. 6, 1942 2,329,560 Seabert Sept. 14, 1943 2,429,470Knowles Oct. 21, 1947 FOREIGN PATENTS Number Country Date 335,329 GreatBritain Sept. 25, 1930 435,670 Great Britain Sept. 25, 1935

